Slurry doser for layer printing in planar chromatography

Hello,
I would like to present one of my project:
I re-purpose a 3D printer to print silica gel layer for planar chromatography.

Chromatography in two sentences is a technique allowing separation of molecules based on their interactions with a stationary phase (here silica gel) and a mobile phase (here toluene). The mobile phase flow through the stationary phase and the molecules that have more affinity with the stationary phase will flow slower than the molecules that have more affinity with the mobile phase, allowing separation.

Here is the abstract of the paper we published on the subject, PM me if you want the pdf as I don't think I can put it here:
On the basis of open-source packages, 3D printing of thin silica gel layers is demonstrated as proof-of-principle for use in planar chromatography. A slurry doser was designed to replace the plastic extruder of an open-source Prusa i3 printer. The optimal parameters for 3D printing of layers were studied, and the planar chromatographic separations on these printed layers were successfully demonstrated with a mixture of dyes. The layer printing process was fast. For printing a 0.2 mm layer on a 10 cm × 10 cm format, it took less than 5 min. It was affordable, i.e., the running costs for producing such a plate were less than 0.25 Euro and the investment costs for the modified hardware were 630 Euro. This approach demonstrated not only the potential of the 3D printing environment in planar chromatography but also opened new avenues and new perspectives for tailor-made plates, not only with regard to layer materials and their combinations (gradient plates) but also with regard to different layer shapes and patterns. As such an example, separations on a printed plane layer were compared with those obtained from a printed channeled layer. For the latter, 40 channels were printed in parallel on a 10 cm × 10 cm format for the separation of 40 samples. For producing such a channeled plate, the running costs were below 0.04 Euro and the printing process took only 2 min. All modifications of the device and software were released open-source to encourage reuse and improvements and to stimulate the users to contribute to this technology. By this proof-of-principle, another asset was demonstrated to be integrated into the Office Chromatography concept, in which all relevant steps for online miniaturized planar chromatography are performed by a single device.

For the moment, we are only printing one layer so 3D printing is a bit exaggerated, however, the auto bed levelling feature was primordial to assure an homogeneous level. Our objective is layers in the sub 50µm range.
The slurry mixture consist of 0.88 g of silica gel (particle size 5-25 µm), 0.12 g of CaSO4 and 3 g of water. Keeping the slurry under magnetic agitation before use is enough to avoid sedimentation. I must explore other recipes and especially the use of polymer binder.
I also create a software in R for GCODE creation and sending to the arduino. It was necessary to give options that make sense for a chemist, like amount of slurry per path which is set indirectly otherwise (At first, I started with OpenSCAD + Slic3r + Pronterface).
In fine, our objective is to make a small machine able to do other steps of the analytical pipeline for planar chromatography. The concept for such machine is named Office Chromatography, it was introduce in 2010 by my professor but didn't exist so far.